The present invention addresses the sector of packaging groups of products using tubular film lengths.
In particular, the invention relates to a machine for forming tubular film lengths capable of being stretched to size, placed over the products and left to return to their original size in such a way as to wrap the products.
The same inventive concept can be applied to the formation of non-stretch or low-stretch film, such as, for example, heat-shrink wrapping film.
At present, a method for forming tubular film lengths from a continuous film that is already tubular in shape is known.
This method, however, has several disadvantages due to the relatively high cost of the tubular film and the impossibility of forming tubes with openings differing in size from those of the original tube.
A method for forming tubular film lengths from a linear film web is also known.
In this case, the linear film web is fed from a roll, cut to size and wound lengthwise, that is to say, about an axis parallel to the direction of feed, around a fixed forming roller until the two longitudinal edges of the film overlap and can be joined to each other, for example by sealing.
This method and the machines that implement it are not free of disadvantages, however.
A first disadvantage is due to the fact that the maximum radial dimension of the tube formed is limited by the width of the film fed.
A second disadvantage is that the elastic behavior of roll-fed film webs is normally directional to varying degrees, although the film tends to stretch better in the longitudinal direction, that is, in the direction of roll unwinding. When the film is stretched, therefore, it is drawn in the direction transversal to the main direction, thus not using the properties of the film to best advantage.
Yet another drawback of prior art methods is that their productivity is low, which means that they limit the overall productivity of the wrapping machinery that includes a station for forming the required lengths of film.
This invention has for its principal aim to overcome the above mentioned drawbacks by providing a high productivity machine that is easily adaptable to different product sizes and that uses the directional mechanical properties of the film to best advantage.